This invention relates to the preparation of 5-amino-1-phenyl-3-cyano-4-trifluoromethyl sulphinyl pyrazole pesticides as defined by formula-I below, and in particular to 5-amino-1-(2,6-dichloro-4-trifluoromethylphenyl)-3-cyano-4-trifluoromethyl sulphinyl pyrazole. This pesticide, known as Fipronil, titled in Pesticide Manual, 13th edition, entry No. 354, is an important insecticide and was invented by Rhone Poulenc (now BASF AG) in 1987.
The known commercial process for the manufacture of this compound uses corrosive and expensive chemicals such as trifluoro acetic acid. This process needs considerable improvement to make it economically viable. Research for an alternative has led to the invention disclosed herein.